Nick Reiner, son of famous director Rob Reiner and Michele Singer Reiner, will be charged with two counts of murder, Los Angeles County authorities told reporters on Tuesday.
If convicted of the charges, which will be filed later on Tuesday, Mr Reiner could face life in prison with no chance of parole, authorities said. He is being held by the LA County Sheriff's Department without bail.
Just before the news conference began, LA police released new photos of Mr Reiner being arrested late on Saturday night near the campus of the University of Southern California.
"Rob Reiner was a brilliant actor and director and iconic force in our entertainment industry for decades. His wife, Michele Singer Reiner, was an equally iconic photographer and producer," LA County District Attorney Nathan Hochman said at the conference. "Their loss is beyond tragic, and we will commit ourselves to bringing their murderer to justice."
Although he was expected to appear in court on Tuesday, Mr Reiner's high-profile lawyer Alan Jackson said his client still needed to be medically cleared beforehand, and that the necessary evaluation had not taken place. Once he is medically cleared, he will be taken to court to be arraigned on these charges, authorities told reporters.
Media reports indicate that Nick Reiner was last seen with his parents at a holiday party thrown by comedian Conan O'Brien on Saturday. Witnesses said the family left the party shortly after an argument broke out between Nick and his father.
Both parents were later found dead with stab wounds, inside their home in the affluent Brentwood neighbourhood of Los Angeles.
Nick Reiner was apprehended by LA police early on Sunday morning and officially named as a person of interest.
Over the years, he has had a public struggle with drug addiction and mental illness. At one point, he assisted his father in the production of a film based largely on his battles with addiction.
The son of comedy great Carl Reiner, Rob Reiner married photographer Michele Singer in 1989. The couple met while he was directing When Harry Met Sally, and had three children together.
Reiner, 78, was one of Hollywood's most prolific directors. His works include some of the most memorable films of the 1980s and 90s, including This is Spinal Tap, A Few Good Men, When Harry Met Sally and The Princess Bride.
His role as Mike "Meathead" Stivic in the 1970s TV classic All in the Family, alongside Carroll O’Connor’s Archie Bunker, catapulted him to fame.
As his Hollywood star continued to rise, so did his philanthropic and political activism, particularly with progressive causes. He helped to raise hundreds of millions of dollars for Democratic candidates.
He was openly critical of President Donald Trump. Shortly after news broke about Reiner's passing, Mr Trump said on Truth Social that he and his wife were killed “due to the anger he caused others”.
“He was known for having driven people crazy by his raging obsession" with the US leader, he wrote.
The lengthy social media post sparked a backlash in both Democratic and Republican circles.
When asked about the anger that had built up throughout Monday in response to his comments, Mr Trump persisted. "I was not a fan of Rob Reiner at all in any way, shape or form," he said.
Reiner was married to actor-director Penny Marshall, best known for her role in the popular sitcom, Laverne and Shirley, from 1971 to 1981. He adopted her daughter, Tracy Reiner.
